Stage for high temperature indentation test

ABSTRACT

An indentation tester and indentation method for testing a sample heated at a temperature range from above 800° C. to 1200° C., and above, is disclosed. The indentation tester includes a stage having a metallic cylindrical base that houses an inner cylindrical base made of a temperature resistant material sufficient to maintain shape over the range of the heating temperature. A removable crown fastens to the cylindrical base and includes a ring that holds an axisymmetric pipe made of a temperature resistant material sufficient to maintain shape over the range of heated temperature. A nut is turned to tighten the pipe which secures the sample and guides an indenter to penetrate the sample. The indenter includes a rod made of temperature resistant material and a indenter tip.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to provisionalapplication No. 62/470,663 filed Mar. 13, 2017, the entire contents ofwhich are incorporated herein by reference.

FIELD OF DISCLOSURE

The present disclosure relates generally to a stage for high temperatureindentation testing that may be used, for example, for indentationtesting at a high temperature such as greater than or equal to 1200° C.

BACKGROUND

Machines like gas turbines operate at temperatures of 1200° C., or more.To aid in operating at these high temperatures, turbine blades arecoated with a thin (nearly 150 microns in thickness) material called aThermal Barrier Coating (TBC). Understanding the mechanical behavior ofthe material at such high temperature is required for design anddurability analyses. Micro-indentation tests and nano-indentation testsare types of tests that can be used to characterize the mechanicalbehavior (e.g., hardness, fracture toughness, scratch hardness, and wearproperties) of thin films such as TBC.

Both a micro-indentation test and a nano-indentation test require aspecial indenter (usually made of a very hard material like diamond orsapphire) to be pressed into a sample whose properties are to bedetermined. Both a micro-indentation test and a nano-indentation testrequire the tip of the indenter to be of a special geometry (e.g.,pyramid, wedge, cone, cylinder, sphere). In each type of test, thesample must be gripped on a testing stage as the indenter tip contactsor penetrates it. However, several challenges arise if the test is to beperformed at high temperatures such as 800° C. to 1200° C., or more,that are required for testing of TBC.

The foregoing “Background” description is for the purpose of generallypresenting the context of the disclosure. Work of the inventors, to theextent it is described in this background section, as well as aspects ofthe description which may not otherwise qualify as prior art at the timeof filing, are neither expressly or impliedly admitted as prior artagainst the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic that shows a stage, according to an exemplaryaspect of the disclosure;

FIG. 2 is a perspective view that shows a first configuration accordingto one example;

FIG. 3 is a schematic of the first configuration in FIG. 2 having ashorter base;

FIG. 4A illustrates a pipe of an indenter stage according to anexemplary aspect of the present disclosure;

FIG. 4B illustrates loading and boundary conditions of a pipe of anindenter stage according to an exemplary aspect of the presentdisclosure;

FIG. 5 is a schematic of a second configuration of the indenter stagehaving an alternative bolting configuration according to an exemplaryaspect of the disclosure;

FIG. 6 is a perspective view of the second configuration of FIG. 5;

FIG. 7 is a schematic of the second configuration in FIG. 5 having ashorter base;

FIG. 8 is a perspective view of a cylindrical base having theconfiguration of FIG. 5;

FIG. 9 is a perspective view of the cylindrical base illustrating alocation where the thin cylindrical base will be inserted;

FIG. 10 is a perspective view of the cylindrical base illustrating theinserted thin cylindrical base;

FIG. 11 is a perspective view of the crown for connection to thecylindrical base;

FIG. 12 is a perspective view of the crown mounted to the cylindricalbase;

FIG. 13 is a perspective view of indenter stage while placing a sampleaccording to an exemplary aspect of the disclosure;

FIG. 14 is a perspective view of the indenter stage having the sample inplace according to an exemplary aspect of the disclosure;

FIG. 15 is a perspective view of an indenter stage while inserting thepipe according to an exemplary aspect of the disclosure;

FIG. 16 is a perspective view of an indenter stage with the pipepositioned to hold the sample according to an exemplary aspect of thedisclosure;

FIG. 17 is a perspective view of an indenter stage and the indenteraccording to an exemplary aspect of the disclosure;

FIG. 18 is a perspective view of the indenter stage while the indenteris lowered into the pipe according to an exemplary aspect of thedisclosure;

FIG. 19 is a perspective view of the indenter stage while the indenteris in contact with the sample according to an exemplary aspect of thedisclosure;

FIG. 20 is a perspective view of the indenter stage illustrating detailsof the thin cylindrical disc and the nut that presses the pipe accordingto an exemplary aspect of the disclosure;

FIG. 21 is an image illustrating temperature distribution in the case ofa steel base, according to an exemplary aspect of the presentdisclosure;

FIG. 22 is an image of von Mises equivalent stress distributionaccording to an exemplary aspect of the disclosure;

FIG. 23 is an image of von Mises equivalent stress in the case of aceramic base, according to an exemplary aspect of the presentdisclosure;

FIG. 24 is an image of von Mises equivalent stress in the case of asteel base;

FIG. 25A shows a model of a conventional clamping mechanism;

FIG. 25B shows loading and boundary conditions of a conventionalclamping mechanism;

FIG. 26A shows mesh and boundary conditions of pipe;

FIG. 26B shows mesh and boundary conditions of a conventional clampingmechanism;

FIG. 27A shows a plot of creep strain over time for current invention;

FIG. 27B shows a plot of creep strain over time for a conventionalclamping mechanism; and

FIG. 28. shows a comparison of creep strain vs. temperature for currentinvention and a conventional clamping mechanism.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout several views, the followingdescription relates to a stage for high temperature indentation testing.

An indenter stage is disclosed for performing a micro-indentation testor a nano-indentation test that can be used to characterize themechanical behavior of thin films such as TBC at a high temperature suchas 800° C. to 1200° C., or more. The stage may include a base thathouses a thin base made of a high temperature resistant material onwhich a specimen, also referred to as a sample, is placed for testing. Acrown, which can be fastened to the base, clamps to the thin base togrip and hold the thin base in place while a heating source (such as ametal heating element including an induction heating coil, ceramicheating element, and/or gas heater, or the like) is used to heat thesample to the high temperature and the indenter penetrates the sample.The crown facilitates the clamping of the sample through its threadedportion which a nut is tightened to in order to push a pipe against thesample (as a result clamping it). The sample, and anything below it (theheat resistant material 102 and the base 101), must behave as a rigidsingle piece in order for the system to be compliant. In another words,if the sample and/or the heat resistant material are placed on top ofeach other without any clamping force the acquired signal from the testwill be faulty/incorrect). Therefore, clamping of all pieces is verycritical for getting accurate experimental results.

A sample for a micro-indentation test may be a few microns in thicknessand may be any width that is at least as large as the size of the tip ofthe indenter. Although the sample may be any material for whichhardness, or other mechanical or physical properties, is to bedetermined, the disclosed high temperature micro-indentation test isprimarily for thermal barrier coating materials for turbine blades.Turbine blades are usually made of super alloy (nickel/cobalt basedmaterial). This super alloy is coated with a ceramic based material thatconsists of a bond coat and top coat. Sometimes the thermal barriercoating (TBC) refers to the ceramic materials (bond and top coats).Otherwise, the super alloy and the ceramic (top and bond coats) arereferred to as TBC or TBC system.

FIG. 1 is a schematic of an indenter stage according to an exemplaryaspect of the disclosure. In one embodiment, the indenter stage may beabout 20 cm in height and about 16 mm in width. However, embodiments maybe 8 to 10 cm in height and 12-15 cm in width. In one or moreembodiments, the indenter stage may include a crown 104, which has athreaded ring 104 a in the center and evenly distributed spokes 104 bextending to an outer rim 104 c. The threaded ring 104 a, spokes 104 b,and outer rim 104 c provide support and position an indenter 107.Although the embodiment includes a circular outer rim 104 c, the outerrim may be any shape that has a geometric center for the threaded ring104 a. In some embodiments, the outer rim 104 c may be formed ofstraight line edges, such as a triangle, a square, a pentagon, ahexagon, or an octagon. The number of spokes 104 b can two or more,which are evenly distributed by the same angle. The outer rim 104 cextends to a lower rim portion 104 e that fastens to the metalliccylindrical base. The lower rim 104 e may be of the same shape as theouter rim 104 c. The connection between the outer rim 104 c and thelower rim portion 104 e may be by way of legs 104 d that correspond inposition to the spokes. Although the outer rim 104 c is shown as beingconnected to the lower rim portion 104 e by legs 104 d, it is understoodthat the legs 104 d may be replaced with a wall that extendssubstantially over a majority of the lower surface of the outer rim 104c, e.g., a cylindrical wall. As described above, the crown 104 holds theheat resistant material 102 in place and facilitates clamping of asample 103 through a nut-thread-pipe arrangement. Also, the crown 104holds an indenter 107. Because the crown 104 is for holding the indenter107 and may be exposed to high heat during a high temperatureindentation test, the crown 104 is preferably made of a material thatcan withstand heat at high temperatures, for example in a range of about300 to 500° C., and remain rigid without becoming deformed.

The indenter 107 for performing the indentation slides within a pipe105, which passes through the threaded ring 104 a. The indenter 107consists of two parts: a holder which is a long cylindrical rod, and anindentation tip (or insert) which is typically made of diamond withpyramid, wedge, cone, cylinder or sphere shape. The indentation tip (orinsert) is attached to the holder (the long rod) which must be made ofhigh temperature resistant material like ceramic by threading or anyother temporary joining method. The holder is actuated by a forceapplication device.

A nut 106 is threaded from inside and is placed on the top of the ring104 a to tighten the pipe 105. The pipe 105 must be made of special heatresistant material such as ceramics. As the pipe being pushed downwardit pushes the sample against the heat resistant base (102). Thisprovides clamping of the sample. An important advantage is that theamount of clamping force exerted on the sample can be manipulated by therotation of the nut. However, the friction between the nut and the pipemay cause the pipe to rotate. This rotation is not needed, and it maycause some undesirable effects on the sample. Therefore, the internalsurface of the nut which is in contact with the pipe may be covered withlow friction material (like Teflon) or a bearing can be mounted there.In an exemplary aspect, the nut 106 may be turned by a motor. Also, themotor may include a motor control device. Another exemplary aspect is anautomatic actuator that pushes the tube.

A base 102 in the shape of a cylindrical disc is housed in the metalliccylindrical base 101. The sample 103 is placed on the cylindrical disc102, which can sustain a high temperature. A top portion 102 a of thecylindrical disc is slightly elevated above the top of the metalliccylindrical base 101 to an extent that the crown 104 can tighten thecylindrical disc 102. The crown 104 may be attached to a stage 101 byone or more bolts (or other fastening means) 108 for ease of access toand replacement of the sample and cylindrical base 102. The bolts may betightened by a nut. Alternatively, the holes for the bolts may bethreaded, so that tightening is made by turning the bolt inside thehole. Any fastening means to attach the crown 104 to the stage 101 mustbe such that no lateral movement of the crown occurs during indentationtesting. It may be possible to fasten the crown 104 to the stage 101 byclamps, such as a vice clamp having a cone-shaped end that can beinserted into the bolt hole.

A heating source (such as a metal heating element including an inductionheating coil, a ceramic heating element, or a gas heater) may be used toheat the sample to temperatures up to and including 1200° C., or more.

FIG. 2 is a perspective view of an example configuration of the indenterstage of FIG. 1. In one or more embodiments, the indenter stage includesa metallic cylindrical base 101 that houses a cylindrical disc 102 madeof high temperature resistant material. Although the base 101 and disc102 are cylindrical, the indenter stage is not limited to this shape.The cylindrical shape is uniform, which simplifies the design of theindenter stage. Other shapes such as cube, or shapes with polygonalbases, are possible. The crown 104 is fastened to the metallic cylinder101, and in this position secures the cylindrical disc 102 (oftemperature resistant material) so that the sample 103 can be heated toa high temperature in a range of 800° C. to 1200° C., or more, while theindenter 107 contacts or penetrates the sample 103. The high temperatureresistant material may be a material that can withstand a temperaturethat is sufficient to melt most metals. Some known high temperatureresistant materials include Niobium, Molybdenum, Tantalum, Tungsten,Rhenium, and alloys thereof which have a melting point that is more than1500° C. High temperature resistant materials also include ceramics.Although ceramic materials are brittle and are weak under tension, theyperform well under compression and are abundantly available. Inembodiments, components that are subject to high temperatures are onlysubject to compression, components including the cylindrical base arepreferably made of ceramic material such as an inorganic ceramicmaterial.

The cylindrical base 101 that houses the cylindrical disc 102 is rigidsuch that force applied by the indenter 107 while the sample 103 isheated to high temperature does not cause the cylindrical disc 102 to bedisplaced. A pipe 105 is tightened against the sample 103 by the nut 106in order to grip and hold the sample 103 in place during indentationtesting. The pipe 105 is also of a high temperature resistant materialso that a constant clamping force is applied to hold the sample 103 inplace during indentation testing under high temperature conditions.

The sample 103 preferably has parallel top and bottom surfaces, andpreferably must be kept parallel to the top and bottom surfaces as muchas possible. The area of the top surface of the sample may be macro size(i.e., 1000 microns or greater) in order to perform multipleindentations in different locations and to allow for easy gripping. Theimpression made by an indenter tip may not exceed 35 microns. Thus, thethickness of the sample 103 should be sufficient to accommodate a 35micron impression. For example, a sample 103 may be one inch square witha thickness of about a half inch. This thickness includes the basematerial, like a super alloy (or substrate) and the coating (on top ofthe base material). The coating itself can be composed of differentlayers such as bond coat and a top coat.

In one embodiment, the crown 104 is arranged with a threaded ring 104 apositioned above the top surface of the disc 102 by a distance that isbased on the size of the pipe 105. The pipe 105 must be shorter than theindenter holder 107. The length of the indenter holder 107 will set thedistance between the sample (which is heated to 1200° C. or more) andthe actuator (and other electronics and parts of the indentationequipment), thus, keeping away from the heat. However, this is notalways the case. For example, if the entire apparatus is placed in avacuum chamber, then only radiation heat transfer is going to beoperative (no convection because there is no air). In that case, ashield can be used to protect the electronics from the heat. The lengthof the pipe 105 should be long enough to allow fixing the sample inplace while it is heated at a high temperature. An outer rim 104 cconnects to the ring 104 a by two or more spokes 104 b extending fromthe threaded ring 104 a at equal angles between adjacent spokes. Theouter rim 104 c is mounted above the disc 102 by two or more legs 104 dcorresponding to the spokes 104 b. A lower rim portion 104 e clamps thedisc 102. Although two bolts 108 are used in this example, there may befour or more bolts, or other fastening means, for bolting/fastening eachleg 104 d of the crown.

FIG. 3 is a cross-section of the example configuration of the indenterstage of FIG. 2 configured with a shorter base. Indenting may beperformed by an indenter 107. The pipe 105 may be clamped by a nut 106that is attached to the crown 104. The pipe 105 passes through the crownring 104 a which applies compressing force to the sample 103 to ensurethe sample does not slide during the indentation test. The pipe 105enables a high temperature resistant rod to pass through and slidewithin the pipe 105. For purposes of micro-indentation ornano-indentation testing, the high temperature resistant rod has adiamond attached to one end of the rod, which together constitute theindenter 107.

FIGS. 4A and 4B describe schematics of the pipe 105. The nut 106 (FIG.3) when tightened applies a compressive force to the pipe 105. In anexemplary aspect, the pipe 105 is axisymmetric and is made of a ceramicmaterial. The ceramic material performs well under compression and theaxisymmetric configuration of the pipe allows a uniform application ofthe compression force. In an exemplary embodiment, a ceramic pipe 105having a length that is about ten times the diameter is sufficient tohandle a compression load that would be applied by the nut 106.

FIG. 5 is a schematic of indenter stage having an alternative boltingconfiguration according to an exemplary aspect of the disclosure.

FIG. 6 is a perspective view of the alternative bolting configurationfor the indenter stage of FIG. 5. FIG. 7 is a schematic of the exampleconfiguration in FIG. 5 having a shorter base. As can be seen in FIG. 2,the crown 104 may be attached to a section at the top of the stage 101by one or more bolts 108. As can be seen in in FIG. 6, the crown 104 maybe attached to a lower portion of the stage 101 by one or more bolts108′.

In an exemplary aspect, both the pipe 105 and disc 102 are made of aceramic material. The use of ceramic material for the pipe and the discenables the sample 103 to be heated to 1200° C. while performing highlyaccurate indentation testing. Also, as mentioned above, ceramic materialdoes well in handling compression load.

In order to perform an indentation test, such as a high temperaturemicro-indentation test or a nano-indentation test, the crown 104 isfastened to the metallic cylindrical base 101. FIG. 8 is a perspectiveview of a cylindrical base 101 having a bolting configuration as shownin FIG. 5. FIG. 9 is a perspective view of the cylindrical base 101illustrating a location where the thin cylindrical disc 102 will beinserted. FIG. 10 is a perspective view of the cylindrical base 101having the inserted thin cylindrical disc 102. Next, as shown in FIG.11, the crown 104 is connected to the cylindrical base 101 using a pairof bolts 108 a, washers 108 b, and nuts 108 c. The bolts 108 a, washers108 b, and the nuts 108 c are used to clamp the crown 104 to themetallic cylinder 101, which in turn, clamps the cylindrical disc 102.FIG. 12 is a perspective view illustrating the crown 104 mounted to thecylindrical base 101. FIG. 13 is a perspective view illustrating a stepof placing the sample 103 on an upper flat surface 102 a of thecylindrical disc 102. FIG. 14 is a perspective view illustrating theindenter stage with the sample 103 positioned at the center of the thincylindrical base 102. Next, as shown in FIG. 15, a high temperatureresistant pipe 105 is inserted in an opening of the crown ring 104 a andis pushed against the sample 103. The threaded nut 106 is placed on topof the ring 104 a and, as shown in FIG. 16, presses the pipe 105 againstthe sample 103 by compressive force. An induction heating coil heats thesample 103 to about 1200° C. During high temperature indentationtesting, the parts that are in contact with the sample must be broughtinto equilibrium such that their temperature is the same as that of thesample. Thus, heat is applied for several minutes to bring the sampleand parts in contact with the sample into temperature equilibrium. FIG.17 is a perspective view illustrating insertion of the indenter 107 intoan opening in the nut 106 and into the pipe 105. FIG. 18 is a schematicillustrating the indenter being inserted, including a rod 107 a and atip 107 b. As shown in FIG. 19, the indenter 107 contacts or penetratesthe sample 103 based on test parameters. FIG. 20 is a perspective viewillustrating a detailed view of the crown 104 applying pressure to thecylindrical disc 102 and a detailed view of how the nut 106 presses thepipe 105 as it is tightened in order to stabilize the sample 103.

Finite element analysis was performed in order to verify the performanceof an example indenter stage according to the present disclosure.However, the present disclosure is not limited to this example. FIG. 21shows the heat distribution in an indenter having a ceramic plate 102 ona steel base 101. As can be seen in FIG. 21, the temperature for thesteel base 101 is between 400 to 500° C. FIG. 22 shows the von Misesequivalent stress distribution. However, the high equivalent stressvalue in FIG. 22 is misleading because contact analysis between ceramicand steel was not defined. In the configuration used in FIGS. 21 and 22,the two pieces were glued and the resulting high stress was due to thedeformation mismatch between the ceramic and the steel. Therefore, tohave a more accurate understanding of the stress levels, focus was madeon the ceramic and the top part of the steel base. The equivalent stressdistribution for the ceramic 102 and the steel base 101 are shown inFIGS. 23 and 24, respectively. These two figures show that the stresslevel is in the range of 350 MPa, which is low.

A major cause of failure in designs is creep. Thus, analysis wasperformed for creep. Creep analyses were performed using ANSYS software.Comparative analysis was made for Anton Parr GmbH High Temperature UltraNonintention Tester UNHT HTV.

The analysis for the Anton Parr Tester included applying a clampingforce by bending loading. A wedge applied clamping force as the crown isadvanced into higher pin position. The clamping wedge was modeled as a2D plain strain plate and its dimensions were roughly estimated based onthe arrangement as shown in FIG. 25A. The loading and boundaryconditions for this wedge are shown in FIG. 25B. Different magnitudes ofdisplacement were considered such that the resulting clamping force iscomparable to the present indenter stage. These displacement magnitudesare 0.01, 0.05, 0.1. 0.15 and 0.2 mm.

The well-known Norton's creep model, Eq. 1, is usedε=A σ ^(p) t ^(q)  (1)

where ε is the creep strain, σ is the stress, t is the time, and A, p, qare material constants as a function of temperature.

Norton's constants were obtained for high strength steel plate attemperatures, 27, 300, 400 and 500° C. only, and only these temperatureswere analyzed in the finite element analysis.

The Norton's constant used in ANSYS software are listed in Table 1. Thefinite element models for the present indenter stage and the Anton Parrarrangement are shown in FIGS. 26A and 26B, respectively.

TABLE 1 Norton's creep constant at different temperatures. SteelProperties Temperature True K E Yield UTS K Constants used in ANSYS (°C.) [GPa] [MPa [MPa [Mpa] C1 C2 C3 1 300 (27) 208 298 590 792 3.4833E−144.505 −0.72072 2 573 (300) 170 254 660 886 2.1016E−14 4.505 −0.72072 3673 (400) 157 231 532 713 5.5922E−14 4.505 −0.72072 4 773 (500) 143 203390 523 2.2589E−13 4.505 −0.72072

Static analyses were performed on both arrangements to investigate therelation between the applied force and resulting displacement. Table 2shows the resulting von Mises stresses and the displacements from theapplication of 1, 2, 3 and 4 N. Similarly, Table 3. Shows the resultingvon Mises stresses and reactions from the application of 0.01, 0.05, and0.1 mm. It can be seen from Table 2 that a force of 4N will result in0.1049E-3 mm of displacement at the location of applied force.Therefore, creep analysis on Model A (the present indenter stage) wasperformed under displacement controlled with applied value of 0.1049E-3mm. This value is corresponding to an applied force of 4N which is highin magnitude. However, it will still be used as the worst-case scenario.

TABLE 2 Static analysis on Model (A)-the submitted design. Load vonMises Stress [MPa] Displacement [mm] [N] Node 9 Node 10 Max. Node 3 Node9 Node 10 1 0.064248 0.63196 0.72919 0.26228E−4 0.26232E−4 2 0.128500.12639 0.14584 0.52456E−4 0.52464e−4 3 0.19274 0.18595 0.218760.78684E−4 0.78696E−4 4 0.25699 0.25279 0.29167 0.10491E−3 0.10493E−3

The analysis on Model B (the Anton Parr Tester) design was performedunder displacement controlled with a value of 0.01 mm. As listed inTable 3, this displacement value will generate a reaction in thenegative y-direction of about 0.37 N which is basically the clampingforce. This is a low value. However, the analysis is performed to showthat even though conservative values were considered for the Anton ParrTester it is still not better than the submitted design.

TABLE 3 Static analysis on Model (B)-the Anton Parr Tester. von Misesstress exceeded the yield strength at 0.15-0.2 mm. Von Mises stressReactions Applied displacement At node 2 Rx [N] Ry [N] 0.01 15.33417.212 −0.37135 0.05 76.670 86.059 −1.8567 0.1 170.05 172.12 −3.7135

As mentioned previously, necessary creep constants were only obtained ata maximum temperature of 773 K (500° C.). The test will run for onecomplete hour.

The evolution of creep strain in x- (EPCRX) and y- (EPCRY) directionsfor the present indenter stage and Anton Parr Tester are shown in FIGS.27A and 27B, respectively. The time (x-axis) is measured in hours. Inaddition, Table 4 lists the numerical values of the creep strain at thecritical locations for both designs and at different temperatures. Torecognize the differences between present indenter stage and Anton ParrTester the data in Table 4 are plotted in FIG. 22. It is clear from FIG.28 that the present indenter stage is significantly more resistant tocreep than the Anton Parr Tester.

TABLE 4 Creep results for: Model (A): present indenter stage and Model(B) Anton Parr Tester. Temperature K (° C.) Node von Mises Creep StrainModel A 300 (27)  3 0.44923E−15 573 (300) 3 0.10923E−15 673 (400) 30.20310E−15 773 (500) 3 0.53862E−15 Model B 300 (27)  2 0.36878E−09 573(300) 2 0.82739E−09 673 (400) 2 0.15384E−08 773 (500) 2 0.40796E−08

The critical components in both approaches are used to apply clampingforce on the sample. Because the sample is heated at certain temperaturethese components must be equilibrated such that their temperatures arevery close to the sample. As the clamping force must be kept constantduring the test, the critical components will be prone to failure due tocreep damage.

The well-known Norton's creep law was used; the obtained results clearlyshow that the present indenter stage is significantly better than thatby Anton Parr Tester.

It was assumed that both designs are made of the same materials.Although this assumption is conservative and in favor to the Anton ParrTester because the submitted design can easily be made of ceramicmaterial that should have significantly better performance in hightemperature applications.

The indenter stage of the present disclosure is better than the AntonParr Tester. The indenter stage of the present disclosure is made ofceramic material which can handle compressive loading. Conversely, theAnton Parr Tester applies clamping by bending which generates tensileand compressive stresses. These forces can each be individuallyeliminated using the indenter stage of the present disclosure. Ceramicsare weaker in tension than in compression making the application ofceramics in Anton Parr Tester less likely (if not impossible). Also,using ceramics in a high temperature application is preferable becauseof its durability, which is better than that of alloys.

A system which includes the features in the foregoing descriptionprovides numerous advantages. In particular, the disclosed stage, andparticularly the approach to clamping, should enable micro- andnano-indentation testing at high temperature reaching to, and exceeding,1200° C.

Numerous modifications and variations are possible in light of the aboveteachings. It is therefore to be understood that within the scope of theappended claims, the invention may be practiced otherwise than asspecifically described herein.

Thus, the foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting of the scopeof the invention, as well as other claims. The disclosure, including anyreadily discernible variants of the teachings herein, defines, in part,the scope of the foregoing claim terminology such that no inventivesubject matter is dedicated to the public.

The invention claimed is:
 1. An indentation tester for testing a sampleheated at a heating temperature above 800° C. to 1200° C., theindentation tester comprising: a stage including an outer base thathouses an inner base made of a temperature resistant material sufficientto maintain shape at the heating temperature; a removable crown thatfastens to the outer base, wherein the removable crown includes asupport that holds an axisymmetric pipe made of a temperature resistantmaterial sufficient to maintain shape over the range of heatedtemperature, wherein the axisymmetric pipe guides an indenter topenetrate the sample, wherein the removable crown includes a first rimthat has a central threaded ring mated with a threaded nut andtightening the nut places a compressive force on the pipe and thecompressive force presses the axisymmetric pipe which pushes against thesample to secure the sample in place.
 2. The indentation tester of claim1, wherein the first rim includes an outer rim that is attached to thethreaded ring by spokes spaced at equivalent angles between adjacentspokes, and legs projecting from the outer rim at positionscorresponding to the spokes, wherein at least two opposing legs arefastened to the outer base.
 3. The indentation tester of claim 2,wherein a top portion of the inner base is elevated above the top of thestage such that the crown presses against the inner base.
 4. Theindentation tester of claim 1, wherein the support that holds the pipeis ceramic.
 5. The indentation tester of claim 1, wherein the outer baseis a metallic base.
 6. The indentation tester of claim 1, wherein theindenter includes a rod made of the temperature resistant material and atip attached to the rod.
 7. The indentation tester of claim 6, whereinthe tip is made of diamond with pyramid, wedge, cone, cylinder or sphereshape.
 8. The indentation tester of claim 1, wherein the indentationtester is a nano-indenter.
 9. The indentation tester of claim 1, whereinthe indentation tester is a micro-indenter.